This proposal is a continuation of the previously awarded grant by National Cancer Institute dealing with molecular structure studies of a series of compounds which are of biological interest by electron diffraction technique and molecular quantum mechanical method. Various N-oxides as well as adenine-l-oxide, purine-N-oxide, and 6, -methyl- purine-l-oxide have been chosen for investigation. The first part of this project was the development and revision of various computational programs for electron diffraction and quantum mechanical calculations. Several highly symmetrical cyclic hydrocarbons have been used for the testing case of the programs and their structures have been reported. The second part of this project is to continue the molecular structure investigation of the proposed heterocyclic N-oxides. In order to understand more about the chemistry of purines and N-oxides, their structural informations deem necessary, since none of the above- mentioned structures has been investigated. The structures of imidazole, and pyrazole will be investigated by electron diffraction. The quantum mechanical calculations will also be continued. The constituents of pyridine-pyrazoles which are being studied in fighting against cancer have been partially investigated. Further structural and quantum mechanical investigations are needed in order to study their chemical reactivities and biological activities.